Hitherto, as an apparatus adapted for discharging liquid, there are liquid discharge apparatuses of the ink jet type system which are adapted for discharging inks which are liquid from liquid discharge portions with respect to a recording paper as object to record images and/or characters.
The liquid discharge apparatuses using ink jet system have the merits that running cost is low, and miniaturization of the apparatus and realization of color print image are easy.
In the liquid discharge apparatuses using ink jet system, inks of yellow, magenta, cyan and black, etc. are delivered from ink cartridge to ink liquid chambers of liquid discharge portion, etc. The inks which have been delivered to the ink liquid chambers, etc. are pressed by pressure generated by pressure generating or producing element such as heating resistor, etc. disposed within the ink liquid chamber. As a result, inks within the ink liquid chambers are discharged from very small ink discharge holes, so-called nozzles provided at the liquid discharge portion. In concrete terms, inks within the ink chamber are heated by heating resistor disposed within the ink liquid chamber to produce bubbles at inks on the heating resistor. By pressure produced by bubbles, inks are discharged from the nozzles to hit the inks which have been discharged onto recording paper as object, etc. to print images and/or characters.
As a liquid discharge apparatus employing the ink jet system, there is a printer apparatus of the serial type in which ink cartridge is loaded or attached to liquid discharge head and the liquid discharge head is moved in width direction of the recording paper, i.e., in a direction substantially perpendicular to carrying direction of the recording paper to thereby hit inks of predetermined colors onto the recording paper. Moreover, there is a liquid discharge apparatus of the so-called line head type in which substantially the same range as width of the recording paper is caused to be discharge range of the ink, i.e., inks are discharged from nozzles of liquid discharge portions arranged in width direction of the recording paper.
In the liquid discharge apparatus of the serial type, when the liquid discharge head is moved in a direction substantially perpendicular to carrying direction of the recording paper, traveling operation of the recording paper is stopped to discharge inks with respect to the recording paper in a stop state while moving the liquid discharge head to repeat such discharge operation to thereby perform print operation. On the other hand, in the liquid discharge apparatus of the line head type, the liquid discharge head is generally fixed to discharge inks from the liquid discharge head with respect to continuously traveling recording paper to hit those inks to thereby perform print operation. For this reason, since the liquid discharge apparatus of the line head type is adapted so that the liquid discharge head is not moved unlike the liquid discharge apparatus of the serial type, it becomes possible to perform high speed print operation as compared to the printer apparatus of the serial type.
Moreover, in the liquid discharge apparatus of the line head type, because it is unnecessary to move the liquid discharge head, respective ink cartridges can be enlarged. As a result, ink capacity of the ink cartridge can be increased. In such liquid discharge apparatus of the line head type, since the liquid discharge head is not moved, simplification of the configuration can be realized. Thus, it becomes possible to integrally provide respective ink cartridges and liquid discharge head.
Meanwhile, in the above-described liquid discharge apparatus of the line head type, print accuracy of image and/or character, etc. depend upon accuracy of the timing at which ink is hit onto traveling recording paper. Explanation will be given in concrete terms. There takes place the problem that when, e.g., traveling speed of the recording paper is high, print operation is performed in the state where recorded images and/or characters, etc. are expanded in carrying direction of the recording paper, and while when traveling speed of the recording paper is low, print operation is performed in the state where recorded images and/or characters, etc. are contracted in carrying direction of the recording paper.
In order to solve such problem, in the liquid discharge apparatus of the line head type, e.g., servo motor, etc. is used for control of motor for traveling recording paper, etc. Namely, traveling speed is caused to be constant so that unevenness does not take place in traveling speed of the recording paper to thereby control the timing at which ink is hit onto the recording paper.
Even in the case where servo motor as described above, etc. is used, while expansion and/or contraction of image, etc. are eliminated, there is the possibility that when there slightly exists error of several microns at impact timing of ink onto the recording paper, color tone unevenness, i.e., unevenness of density of color may take place in carrying direction of the recording paper. In concrete terms, when control of traveling speed of the recording paper by servo motor is delayed slightly by several microns, color tone becomes thick at this portion. On the other hand, when control of the traveling speed of the recording paper by the servo motor becomes fast slightly by several microns, color tone becomes thin at this portion. Further, when control of traveling speed of the recording paper becomes fast at level of several ten microns or several hundred microns, there take place a portion in which no ink is hit, i.e., so-called white stripe would take place over the range in a direction substantially perpendicular to carrying direction of the recording paper.
On the other hand, in the liquid discharge apparatus of the serial type, in stopping traveling operation of the recording paper to perform print operation, print operation in which so-called overlap portion is provided is performed in such a manner that the previous print portion and current print portion overlap with each other within a predetermined range at the boundary portion thereof to thereby prevent color tone unevenness or white stripe from taking place in carrying direction of the recording paper. In the liquid discharge apparatus of the serial type, color tone unevenness and/or white stripe, etc. can be suppressed, but there is the problem that the above-mentioned overlap portion is provided so that time required for print operation is elongated, and/or quantity of ink used for print operation is increased.
In order to solve problems as described above, it is proposed in the Japanese Patent Application Laid Open No. 2000-185403 publication that there is employed (used) such a configuration disclosed in the U.S. Pat. No. 5,172,139 specification, i.e., the configuration in which plural heating resistors are provided so that they are face-symmetrical with each other at a plane including center line of nozzle at a position opposite to nozzle of the liquid discharge portion which discharges inks to allow heat quantities of respective heating resistors to be different from each other to thereby control discharge direction of ink.
In the case of the configuration disclosed in the Japanese Patent Application Laid Open No. 2000-185403 publication, in the case where heat quantities of respective heating resistors are not suitable, ink might not be discharged in a desired discharge direction. As a result, picture quality may be lowered. In practical sense, as in a liquid discharge portion (element) 201 shown in FIG. 22, in the case where energies delivered to the respective heating resistors 202 are not suitable, balance of size of bubbles 204, etc. that the respective heating resistors 202 produce at ink 203 becomes poor. Namely, in this liquid discharge portion 201, there is the possibility that balance of pressure for pressing ink 203 on respective heating resistors 202 becomes unstable so that discharge direction of ink may be diverse.
Moreover, in the liquid discharge portion 201, in the case where balance of pressure for pressing ink 203 on respective heating resistors 202 becomes unstable, there are instances where discharge angle θ of ink droplet i from the nozzles 205 becomes too small. In this case, in the liquid discharge portion 201, since discharge angle θ of ink droplet i becomes too small, ink droplet i comes into contact with edge portion 205a of the nozzle 205 when the ink droplet i is discharged from the nozzle 205. Further, the discharge direction is caused to be diverse.
From the above-mentioned facts, in the discharge portion (head) 201, there are instances where impact point is shifted when ink droplet i is hit upon the principal surface of the recording paper P, and color tone unevenness and/or white stripe, etc. take place so that picture quality may be lowered.
In view of the above, in the liquid discharge portion 201, it is important to suitably control heat quantities of respective heating resistors 202 for discharging ink droplet i from the nozzle 205, i.e., energy quantities, etc. such as current, etc. delivered to respective heating resistors 202 for the purpose of heating respective heating resistors 202.